The present invention broadly relates to recording devices or recorders, and, more specifically, concerns a new and improved surface structure for the drum of a recorder.
Generally speaking, the drum of the recorder is constructed as a negative pressure-hollow cylinder which is mounted to be rotatable about its lengthwise axis within a recorder. At the outer cylindrical circumferential surface of the drum body there is provided a clamping portion arranged essentially parallel to the lengthwise axis of the drum and serving for the retention of a sheet-like record carrier. Additionally, at the outer cylindrical circumferential surface of the drum body there are provided a plurality of channels which extend essentially parallel to the clamping portion, these channels being distributively arranged at the circumference of the drum body and flow communicating by means of openings with the interior of the drum.
In U.S. Pat. No. 4,101,018, granted July 18, 1978 there is disclosed a drum for a recording device which is constructed as a hollow cylinder and operatively connected with a suction device. At the outer circumferential surface of the drum jacket there are provided uniformly distributed channels arranged parallel to the lengthwise axis of the drum and in each individual channel there are provided a number of bores which penetrate the drum jacket or shell and are arranged at a spacing with respect to one another. By means of the negative pressure prevailing at the outer circumferential surface of the drum jacket a sheet-like record carrier or medium is retained at the outer circumference of the drum.
In German Patent Publication No. 3,000,887, published Aug. 7, 1980 and the corresponding U.S. Pat. No. 4,285,507, granted Aug. 25, 1981, there is disclosed a recorder constructed as an ink jet printer. A drum is provided for retaining a sheet-like record carrier. The drum is provided with internal chambers which communicate with a vacuum line and with a number of openings uniformly distributed at the circumference of the drum. These openings are arranged in a row in the axial direction of the drum and penetrate through the drum jacket or shell. By means of these openings there can be applied a negative pressure to the outer circumferential surface of the drum, by means of which there can be retained the record carrier bearing at the circumference of the drum.
With the state-of-the-art drum constructions there is required a relatively high suction capacity of the suction device in order to realise a stable position of the record carrier or medium at the cylindrical drum surface. Particularly when there are being handled smaller record carriers or mediums which bear at the drum surface over a limited lengthwise extent and throughout a limited angular region the openings and channels which are not covered by the record carrier suck-up a relatively large amount of air. Consequently, there is required a high suction output, and thus, a large size suction device. Additionally, with the heretofore known constructions of drums there is not insured for a reliable contact of the record carrier at its end region.